1. Field of the Invention
The present invention relates to a registration processing apparatus, a registration method, a program and a storage medium for performing computer processing on plural image data and performing image registration.
2. Description of the Related Art
In medical fields, a doctor displays a medical image obtained by imaging a patient on a monitor, performs interpretation of the displayed medical image, and thereby observes the status or temporal change of a morbid portion. As an apparatus to generate this type of medical image, a simple X-ray machine, an X-ray computed tomography (X-ray CT) machine, a (nuclear) magnetic resonance imaging (MRI) machine, nuclear medicine diagnostic systems (SPECT, PET and the like), a diagnostic ultrasound (US) system, and the like, can be given.
Further, a diagnosis may be conducted by utilizing plural images obtained from plural apparatuses for the purpose of higher accuracy diagnosis. For example, information useful in diagnosis and medical treatment such as laser radiation can be obtained by imaging one subject using plural imaging apparatuses, and superposing obtained images.
For example, a more accurate position for laser radiation as medical treatment can be obtained by superposing an image obtained from a diagnostic ultrasound system with a three-dimensional image obtained from a CT machine. Accordingly, high accuracy in image superposition is required. However, under the present circumstances, doctors perform image registration between both images by visual observation.
On the other hand, a method for high-speed image registration is studied (Document 1. “2D-3D Registration Using 2D Distance Maps” by Yumi Iwashita, Ryo Kurazume, Kenji Hara, Naoki Aburaya, Masahiko Nakamoto, Kozo Konishi, Makoto Hashizume and Tsutomu Hasegawa, Meeting on Image Recognition and Understanding 2005 (MIRU2005)).
In this method, a relative position between both images is estimated by calculation in the following 1) to 4) until the respective values are converged:
1) to extract a contour line of a two-dimensional image and generate a distance map indicating a value corresponding to a distance from the contour line;
2) to obtain the contour of a silhouette image of a three-dimensional geometric model, and apply a force calculated in correspondence with the distance map to a contour point;
3) to obtain the sum of forces applied to all the contour lines and moment about the center of gravity of the three-dimensional geometric model; and
4) to update the position and attitude of the three-dimensional geometric model in correspondence with the obtained force and moment.
As the technique disclosed in the above Document 1 lacks an idea of indicating a distance map indicating a value corresponding to a distance from a contour line with an expression, it is necessary to store the value indicating the distance map into a memory. Upon calculation of, for example, the force in 3), processing for obtaining coordinates of the silhouette image of the three-dimensional geometric model on the memory corresponding to the contour coordinates is required. Accordingly, it is impossible to obtain a solution of numerical calculation without access to the memory. Further, to realize efficient registration, limitation of memory access disturbs simplification of calculation. This influences registration accuracy.